Method for manufacturing improved magnetic articles



May 2, 1961 s. D. Howe 2,982,678

METHOD FOR MANUFACTURING IMPROVED MAGNETIC ARTICLES Filed June 25, 1958 METHOD FOR MANUFACTURING IMPROVED MAGNETIC ARTICLES Spencer D. Howe, Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of .Delaware Filed June 23, 1958, Ser. No. 744,890 6 Claims. (Cl. 148-103) The invention and the discovery hereof relates generally to the field of handling, treating and forming metallic alloys for ultimate use in connection with the manufacture of permanent magnet articles and relate more specifically to a'method for making magnetic articles from vanadium-iron-cobalt alloys.

In the formation and manufacture of permanent magnets and particularly in connection with the manufacture of such magnets that are intended for use in hysteresis type clutches, motors and the like, and wherein good magnetic properties, relatively easy machineability and precision parts are desired, it is important that a material be selected that will provide a satisfactory compromise for the desirable characteristics. For this purpose, aluminum-nickel-cobalt alloys have been employed, together with certain types of cobalt steel, iron and other alloys thereof. loop for the various available magnetic materials and alloys, it is important that the squareness factor i.e., the area of the loop divided by the area of a circumscribed rectangle be such as to provide the largest peak value of squareness factor to obtain a structure having the smallest over-all volume. In connection with devices and magnets employed to produce ux across a fixed air gap such as in loud speaker magnets, a material having the highest BH product will require the smallest volume of magnetic material. is commonly taken as a figure of merit for permanent magnet materials. A maximum (B XH product is not usually determined from considerations of the labor involved. Generally, it has been lthe practice merely to obtain the remanence B, and coercive force Hc. The product of Br XHC is higher than the maximum B XH, although such product is roughly proportional theretol Additionally, for the same BTXHe of two materials, the material having the higher Br is preferred. Accordingly, both the product of BIXHc and the squareness factor indicated hereinbefore may be used as indexes defining figures of merit.

The maximum energy product -is generally proportional to the loop area when the material is driven to saturation during magnetization thereof; however, inhysteresis devices the material is not driven to saturation, inasmuch as such action would result in excessive weight or power input per torque output. For hysteresis devices,

`the loop area, as a function of excitation, provides the most convenient design parameter.

Further, in the selection of a material for the purposes defined it is also important that the ratio of the volume of magnetic material to the volume of copper coil windrings employed in an exciting electromagnet be considered. This is particularly important when considering various materials for use in structures such as hysteresis, motors and clutches that may be employed with gyroscope torqueing mechanisms and particularly such mechanisms that are adapted for use in aircraft, missiles and When considering the usual hysteresis,

This statement of maximum energy product` States Patent O 2,982,678 Patented May 2, 1961 For the purposes intended, it has been found that vanadium-iron-cobalt alloys, commonly known as Vicalloy I, provide the desired machineability together with reasonably satisfactory magnetic properties. Material of this type is discussed in Patent Number 2,190,667, issued to G. A. Kelsall et al. on February 20, 1950. It has also been indicated that improved magnetic properties may be obtained in connection with vanadiumiron-cobalt alloys by cold working the material prior to final stage of heat treatment. Apparently, these improved magnetic characteristics are obtained due to grain orientation and are particularly established in one direction. Such cold working has taken the form of swaging, rolling, drawing, etc., with the drawing technique being the most effective. However, such drawing or other cold working has required the use of massive and powerful equipment to produce forcible elongation in the nature of the drawing of a 1/2" diameter bar down to 1A" diameter or the like. Such cold'working is difficult and expensive. Moreover, since the improvement in magnetic properties is realized only in the direction of elongation, the drawing process cannot be applied to parts wherein the magnetic flux is to follow a closed circle within the material, such as the ring of active material in a typical hysteresis clutch, wherein the flux path is circumferential. In other words, cold working techniques are applicable to permanent magnets that are vemployed to produce flux across a fixed air gap but are not satisfactory forV use in the manufacture of structures employed in a hysteresis device.

It is accordingly one object of the present invention to provide a method of forming articles from vanadiumiron-cobalt alloys or other similar material and wherein improved magnetic properties result following magnetization thereof.

It is another object of the invention to provide a method of manufacturing magnetic articles having improved magnetic properties, together with relatively easy machineab-ility.

It is still another object of the invention to provide a simplified, relatively inexpensive method of manufacturing articles for use as permanentk magnets.

Other and further important objects 'of the invention will become apparent from the disclosures in the following specification and discussion, appended claims and ac-l companying drawing, wherein:

Figure l is a perspective view of a ring shaped article that may be made by the process of the present invention;

Fig. 3 is a ow chart illustrating the various general steps of the present process; and

Fig. 4 is a graph showing the characteristics of different types of material manufactured by and without the process steps of the present invention.

In practicing the present invention, Vcobalt alloy material havingy generally 6 to 16' percent vanadium, 30' to 52 percent iron and 36 to 62 percent cobalt' is employed. More specifically, it has been found that the material containing approximately l0 percent vanadium, 40 percent iron and 50 percent cobalt and including approximately '1% percent impurities, is satisfactory for the intended purposes. As shown in Fig. l, the material isv initially formed in the shape of a ring as by any known methods such as, for example, by casting or through utilization of forged tubing of the desired material, The initial material is relatively hard and difficult to machine other than by grinding. Ob-

the like, and wherein weight factors must be a serious consideration.

viously, grinding operations are slow and expensive. Accordingly, it has been found that the ultimate completed cost of the article is less when employing vforged vanadium-irontubing, rather than an initially cast part and, from the forged tubing, the ring may be cut to the approximate length desired. Thereafter, the ring is annealed by heating to between 800 C. and 1300o C. and water quenching. In this connection, it has beenfound -that Vheat treating to approximately 1000 C. is satisfactory forappropriate annealing of the ring. Following the heating, the ring isquenched 4to a temperature somewhat below 600 C. (may be Vroom temperature) lin water. It has been found that a water quench is preferable to an oil quench, inasmuch-as less oxidation scale is thus produced on the ring than would otherwise be induced by oil. Additionally, a sodium hydroxide solution may be used, thus to produce considerably less scale than would be encountered with either water or oil.

Following the heat treating as indicated hereinbefore, the material will have a Rockwell hardness (scale C) of from 30 to 32, thus making the material sufficiently soft as to permit relatively easy machining thereof. The ring may thereafter be machined in the usual manner to produce the desired ultimate shape. In practice, `for one specific design of hysteresis brake, rings of this type have been made that are approximately 3 inches in outside diameter with a .060 inch wall thickness and .700 of an inch in length. The particular machining operation is carried out to the desired dimensions leaving slight grinding stock and slight extra material to account for a small amount of anticipated growth that will occur in the subsequent heat treating to be described hereinafter. The inner diameter of the ring is, however, held to precise dimensions for a purpose to be hereinafter more fully described.

After the ring has been machined to the desired size and to include the allowances set forth above, a plug is disposed therein. A particular ring and one form of plug is shown in Fig. 2. In this particular form, the plug is of a slightly tapered type; however, in practice, it has been found that a cylindrical plug having an outer diameter suicient to create an approximately .005 inch per inch of diameter interference fit with the inner diameter of the ring is more advantageous. To facilitate entry of such a plug, an end may be chamfered and suitable limit shoulders may be provided, if desired. In the present instance the plug is preferably made from stainless steel and a disposed into the ring by means of a press or similar device. It has been found that shrink fitting techniques are unacceptable for disposing the plug within the ring, inasmuch as the vanadiumiron-cobalt alloy has a tendency rst to expand upon heating and thereafter rapidly to shrink.

With the plug disposed within the ring, it may be seen that the ring is effectively retained against shrinkage. The ring may thereatfer be hardened by baking in a suitable furnace for several hours. It has been found that 41A. to 5 hours is sufficient for such bake hardening with the temperature being held to approximately 600 C. The length of the baking time is not particularly critical in that approximately 90 percent of hardening of the vanadium-iron-cobalt alloy occurs Within the first 1/2 hour of the bake hardening and, after approximately two hours of such hardening, very little increased hardening will be obtained by prolonged baking. When the ring and plug combination are removed from the furnace following the bake hardening step, the ring will have a Rockwell hardness (scale C) of approximately 66.2.

The ring and the plug combination are next permitted to air cool and the plug is removed from the ring. In this connection it would normally be assumed that,

' when using vanadium-iron-cobalt allo-ys, the ring would have shrunk tightly upon the plug as to make it necessary to utilize presses or other means to remove the plug from the ring, this assumption being particularly proper in view of the fact that a press was employed to install the ring'on the plug. It is known that the particular vanadium-iron-cobalt alloys will shrink approximately .005 inch per inch during the bake hardening operation; however, it has been discovered that, through use of the present restraining means for the specific ring during the bake hardening step, such shrinkage does not occur during the bake hardening. `On the contrary, the ultimate ring actually expands approximately .002 inch per inch over the plug diameter even though the plug is disposed within the ring with a strong interference tit. This expansionis caused by the difference between expansion coefficients of Vvanadium-ironcobalt alloys and stainless steel, the expansion of stainless being greater over the particular temperature range used herein. Thus, forcible elongation of the ring is in the nature of only approximately .007 inch per inch, this being a relatively small amount as compared to prior techniques 'teaching elongation of 3 inches per inch and requiring heavy equipment.

Inasmuch as only a relatively small amount of dimensional growth occurs in the article made from the vanadium-iron-cobalt alloy material, it is .thereafter completely practical to complete manufacture of the article by simple grinding operations and removal of only an extremely small amount of material. In most instances it has been found that the plug may be removed from the ring with extreme ease and may, in some instances, require only a slight tapping to loosen the ring from the plug due to the presence of a small amount of scale that may form on the ring during bake hardening thereof. In some instances it is also only necessary to remove the surface scale from the ring in the grinding operation to bring the finished article into the range of desired dimensional tolerances thereof.

In actual practice, the completed ring article made by the process of this invention is permanently magnetized during its use in a hysteresis clutch; however, it is to be understood that the article may be separately magnetized by known methods without departing from the spirit and scope of the invention.

Following completion of the ring article it has been found that, not only has manufacturing and machining been facilitated and dimensions maintained during the two step heat treating process, but also, and of greatest importance, substantially improved magnetic properties are obtained, there being an increase of approximately 20 percent in the hysteresis loop area which deiines the energy per cycle. This particular increase in the hysteresis loop area is indicated in the chart of Fig. 4 wherein different types of materials have been set forth. It is to be noted that, on cast material, a considerable .improvement has been obtained; however, excellent and even better results are obtained utilizing forged tubing for the original material and precipitation or bake hardening on/ or in connection with the plug utilized herein. Also, forged tubing that has been solution annealed and then hardened has shown increased magnetic properties, as defined by increased hysteresis loop area, when manufactured in accordance with the steps of the present invention.

From a different standpoint and in order further to set forth improvements gained through use of the present manufacturing process, it has been found that the specific ring deiined herein, and used in a hysteresis clutch, has enabled a torque output from a specific torqueing apparatus of approximately 4.2 in./lbs., rather than previously obtained approximately 2.5 in./1bs. of torque produced by identical size structures employing hysteresis rings made from different permeable materials.

While the present manufacturing andheat treating techniques have been described in connection with a specific material such as the vanadium-iron-cobalt alloy, it is .to be understood that the present process may be practiced with other alloy materials of such a nature as to be capable of precipitation hardening.

Accordingly, the present invention has achieved approximately 1/z of the improvements realized by the processes of the prior art with only approximately 1/500 of the forcible elongation that has been required by prior art processes, this effect being due to the particular arrangement of steps of the process and to the particular time during the heat treating cycle at which the distortion of the article takes place. Additionally, the present process provide a means for substantially improving the magnetic properties of vanadium-iron-cobalt alloys without the use of heavy, expensive and powerful drawing or rolling equipment.

Having thus described the invention and the present specific embodiment of the method thereof, it is desired to emphasize the fact that modifications may be resorted to in a manner limited only by a just interpretation of the following claims.

I claim:

1. A method for manufacturing an article from alloys having 616% vanadium, 30-52% iron and 36-62% cobalt and for use in magnetic apparatus comprising, the steps of: subjecting said article to heat treating at 800 to 1300% C.; thereafter quenching said article; bake hardening said article at approximately 600 C. for several hours; and simultaneously with said bake hardening restraining said article against shrinkage.

2. A method for manufacturing a magnetic article from alloys having 6l6% vanadium, 30-52.% iron and 36-62'% cobalt comprising, the steps of: subjecting said article to heat treating at 800 to 1300 C.; thereafter quenching said article; bake hardening said article at approximately 600 C. for several hours; simultaneously with said bake hardening restraining said article against shrinkage; and magnetizing said article.

3. A method for manufacturing an article from alloys having approximately 10% vanadium, 40% iron and 50% cobalt and for use in magnetic apparatus comprising, the steps of: subjecting said article to heat treating at 800 to 1300 C.; thereafter quenching said article; disposing a steel restraining member in intimate contact with surfaces of said article; heat bake hardening said article together with said restraining member at approximately 600 C. for several hours; and removing said restraining member from said article.

4. A method 'for manufacturing a magnetic article from alloys having approximately 10% vanadium, 40% iron and cobalt comprising, the steps of: subjecting said article to heat treating at 800 to 1300 C.; thereafter quenching said article; disposing a steel restraining member in intimate contact with surfaces of said article; bake hardening said article together with said restraining member at approximately 600 C. for several hours; removing said restraining member from said article; and magnetizing said article.

5. A method for manufacturing a magnetic article from alloys having approximately 10% vanadium, 40% iron and 50% cobalt comprising, the steps of: subjecting said article to heat treating at 800 to 1300 C.; thereafter quenching said article; disposing a steel restraining member in intimate contact with surfaces of said article; `bake hardening said article together with said restraining member at approximately 600 C. for several hours; cooling said article and said restraining member; removing said restraining member from said article; and magnetizing said article.

6. A method for manufacturing a ring shaped magnetic article from alloys having approximately 10% vanadium, 40% iron and 5 0% cobalt comprising, the steps of: subjecting said article to heat treating at 800 to 1300o C.; thereafter oil quenching said article; disposing a steel restraining member in intimate contact with an inner surface of said article to restrain said article against shrinkage; bake hardening said article together with said restraining member at approximately 600 C. for several hours; air cooling said article and said restraining member; removing said restraining member from said article;

and magnetizing said article.

References Cited in the tile of this patent UNITED STATES PATENTS 2,527,983 Brown et al. Oct. 31, 1950 

1. A METHOD FOR MANUFACTURING AN ARTICLE FROM ALLOYS HAVING 6-16% VANADIUM, 30-52% IRON AND 36-62% COBALT AND FOR USE IN MAGNETIC APPARATUS COMPRISING, THE STEPS OF: SUBJECTING SAID ARTICLE TO HEAT TREATING AT 800* TO 1300%C., THEREAFTER QUENCHING SAID ARTICLE, BAKE HARDENING SAID ARTICLE AT APPROXIMATELY 600*C. FOR SEVERAL HOURS, AND SIMULTANEOUSLY WITH SAID BAKE HARDENING RESTRAINING SAID ARTICLE AGAINST SHRINKAGE. 